Autism Spectrum Disorder (ASD) has historically been diagnosed more frequently in males than females. One explanation for this is the 'female protective effect': that there is something inherent in being female that makes girls and women less susceptible to ASD.Another possibility is that ASD is under-diagnosed in girls and women, due to the existence of a 'female autism phenotype', which is not well captured by current, male-biased diagnostic criteria. To evaluate the 'female protective effect' and 'female autism phenotype' hypotheses, this narrative review describes recent developments exploring the genetic underpinning and behavioural expression of ASD in females. We then look at ways to better identify females with ASD who may be missed under the current diagnostic criteria.
KeywordsAutism, Autism Spectrum Disorders, Gender Differences, Sex Differences, Genetics,
Diagnosis, Person-Environment Fit
IntroductionAutism Spectrum Disorder (ASD) is a group of neurodevelopmental conditions characterised by deficits in social communication and reciprocity, and by restricted and repetitive interests and behaviours 1 . ASD is the current term used to integrate the previously separate diagnostic categories of autistic disorder, Asperger's disorder, childhood disintegrative disorder and pervasive developmental disorder -not otherwise specified (aka 'atypical autism' [2]). ASD is a lifelong condition that is present from birth. Although adult diagnosis is possible, symptoms must be reported as present from early developmental stages in order for the 1 In line with preferences from a majority of the autism community [1], we use identity-first language (e.g. 'autistic person') to refer to individuals with an ASD throughout this paper, while recognising that others might prefer person-first language (e.g. 'person with autism').
Gender differences in diagnosisASD affects approximately one to two per cent of the population [3,4], and is much more likely to be diagnosed in males than in females. Gender ratios in diagnosis vary depending on the country, cohort, and characteristics of those included, but average ratios are reported at around four males for every one female [3][4][5]. However, when looking at those individuals with intellectual disability, the male-to-female ratio narrows significantly to around two-toone [6]. In addition, population-based studies, which screen all participants in order to identify cases regardless of whether they have already been diagnosed by local services, suggest that the male-to-female ratio is closer to 3:1 [7,8]. This is in contrast to the average of around 4-5:1 generally reported in studies based on clinically-diagnosed cases [9]. The fact that a lower proportion of females are found in clinical samples than in community-based, epidemiological samples suggests that there is a bias against autistic girls and women coming to clinical attention. This bias may have existed from the very first conceptions of ASD; only 3 of 11 children in Kanner's original cases were female, and no gi...